1. Field of the Invention
The present general inventive concept relates to a torque limiter, and particularly, to a torque limiter including a clutch spring.
2. Description of the Related Art
A torque limiter is a device that decouples a driving force of a driving unit from a driven unit when a load by the driven unit exceeds a preset range. A torque limiter including a clutch spring has a simple structure, and, thus, the torque limiter is widely used in, for example, cars, electronic products, printers, and duplicators. For example, in a paper feeder for a printer, a torque limiter including a clutch spring is utilized in a power transfer unit for a reverse roller in a paper separator that separates paper sheet by sheet.
FIGS. 1 and 2 illustrate an example of a conventional torque limiter including a clutch spring. Referring to FIGS. 1 and 2, a clutch spring 30 is coupled to a hub 20 receiving a driving force from a driving source (not illustrated). The clutch spring 30 applies a predetermined torque to an outer circumstance of a hub 20. A driven body (not illustrated) is connected to a housing 10. The housing 10 includes catch portions 11 and 12 that are engaged with end portions 31 and 32 of the clutch spring 30. When the hub 20 coupled with the clutch spring 30 is inserted in the housing 10, both end portions 31 and 32 of the clutch spring 30 are engaged with the catch portions 11 and 12, respectively. Thereafter, a cap 40 is coupled to the housing 10. If clearances exist between the end portions 31 and 32 of the clutch spring 30 and the catch portions 11 and 12, an assembly process may be facilitated, but the torque limiting operation of the torque limiter is delayed by a time period corresponding to the distance that must be traversed by the housing to engage with the clutch spring 30. To operate the torque limiter without backlash, there must be no clearances between the catch portions 11 and 12 and the end portions 31 and 32 of the clutch spring 30. Thus, an interval between the catch portions 11 and 12 must be greater than that between the end portions 31 and 32 of the clutch spring 30. In this case, when the hub 20 coupled with the clutch spring 30 is assembled into the housing 10, the end portions 31 and 32 of the clutch spring 30 must be spread out so as to be engaged with the catch portions 11 and 12, which makes the assembly process very inconvenient.
Because a threshold torque of the torque limiter is dependent upon a coupling force between the clutch spring 30 and the hub 20, the threshold torque is affected by manufacturing tolerances of the clutch spring 30 and the hub 20. The torque limiter having the structure illustrated in FIGS. 1 and 2 does not include a structure for compensating for the manufacturing tolerances of the clutch spring 30 or the hub 20. Thus, the manufacturing tolerances of the clutch spring 30 or the hub 20 affect the threshold torque.